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add a component to the bottom of a PCB?

Rink 7 years, 3 months ago

+1 - would be handy (although not essential) for a project I'm working on right now.

Jonathan Cohen 7 years, 3 months ago

Hi Rink,

This is already available for SMD parts only in the current release. THT parts will be a later release.

- j

Rink 7 years, 3 months ago

Cool. Lol. I'm so bad at keeping up with your developments. :)

bootchk 7 years, 1 month ago

My project is a very small two-sided board with all SMD parts.  I'm using version 7.10b.

To clarify what you can apparently do:  I could place a pad on the bottom, and route wires from it to vias.  Then I tried to place an FET in the SMD SOT-23 package on the bottom.  It appears that the three lands are on the bottom (they are dark orange).  However, I could not route from those pads to a via.  (The lands of an SMD part on the bottom cannot be routed from the top or the bottom.)

To restate: if you are speaking of 'SMD parts' in the general sense, you can place them on the bottom of a two-sided board, you just can't route to their lands.  An exception is: 'parts' that are just pads.

If that is the case, for a very small design, could you make a functional PCB (if you don't care about the schematic or breadboard) by putting a pad overlapping the lands of SMD parts on the bottom (and routing from vias to those pads)?  I tried Export for PCB and the PDF files apparently have correct copper on the bottom, with the lands for the SMD parts, the pad, and the vias.  Also, I'm wondering if the Fritzing Fab would reject such a design, where the schematic and breadboard was a garbled mess, but the designer was confident that the PCB was OK. 

My project is the smallest board Fritzing would let me make, 12.7 mm square with only 4 parts, one of which I want on the bottom.  Until now, I have been deadbug soldering the parts together, but now I desire a tiny PCB board.  I suppose such a use case is very rare among Fritzing users.

Jonathan Cohen 7 years, 1 month ago

Hi Bootchk,

You should be able to draw traces from SMDs on the bottom layer.  Make sure the bottom layer is active (there is a button for toggling the active layer in the button bar at the bottom of the window).

I would also recommend upgrading to 0.7.11, since I think I remember some bug in this regard in 0.7.10.

- j

bootchk 7 years, 1 month ago

OK, I will upgrade.  There have been a few posts about this subject.  Most seem to say you can only put a SMD part on the bottom of a single-sided PCB (but I want a double-sided board, with SMD parts, routable, on both sides.)  If that has changed, I don't know when it changed.  But I will try it.

Jonathan Cohen 7 years, 1 month ago

SMDs on the bottom layer of a two-sided board have been available since 0.7.9.  There are two ways to place an SMD on the bottom.  

1. If you have an SMD already on the top layer of your sketch, use the 'layer' drop-down in the Inspector to switch it to the bottom layer.

2. if you have a through-hole part in your sketch, make the bottom layer the active layer, then use the Inspector to change to an SMD package.

- j

bootchk 7 years, 1 month ago

I upgraded.  I still can't route to an FET in a SMD SOT-23 package on the bottom, but I see that I can route to a capacitor in the SMD 1206 package, on the bottom.  So now I suspect that the FET part is one that I made, and I failed to make it properly.  I will study the problem and get back to you.

bootchk 7 years, 1 month ago

The part that won't route on the bottom is one I created with my program "Fritzing Part Scavenger" which creates a "Mystery SMD" family part from any PCB SVG file in the Fritzing directory that it thinks is an SMD footprint with the chosen number of pins.  I could not debug what I am doing wrong in creating the part .fzp file.  But since it seems like Fritzing is moving away from .fzp files (keeping most data in a SQL db) I am not going to debug it further.  I don't understand some nuance about the .fzp files.

But, when I run my bad part through the Part Editor (making some trivial change and then saving it), after that the part routes on the bottom (little square appear on the pins and I can drag from them.)  And any new instances of the part are routable.  My conclusion is that there is some subtle difference between an imported part and a part that the Parts Editor writes back to the db?

For my project, I just used existing parts (transistor and resistor) with SMD packages, even though they are not really the parts I want (a diode and other 3-pin chips) and one SMD package (805) is adequate but not really the best SMD package (say SOD323 for a diode.)

I still think the idea of the Fritzing Part Scavenger is useful, at least for the use case of users working in SMD.  I don't really want to use the Parts Editor every time I need a new SMD package, when they are already out there and have the right number of pins and often the right pins names in the SVG PCB file.  For example, the SOD323  (SMD package for a diode) SVG file is in the Fritzing directories (I think it was gleaned from GEDA) but I don't know where it is attached to any part and it isn't under the "Rectifier" part where I expected it.   I know I could find it using a file browser, and use the Parts Editor to create a new part pointing to that SVG PCB file.  The Fritzing Part Scavenger finds it for you and does all the work (if it didn't have this bug, and if the Fritzing Part Scavenger was packaged better for distribution.)

Also, you could easily extend the File Part Scavenger to change the pinout of a part, which is another common use case.

Thanks for your work.